1. Field of the Invention
The present invention relates generally to valve systems for bleeding pressure from substantially closed chambers, such as the bonnet chambers of valves, conduit sections and the like. More particularly, the present invention concerns by-pass studs having a valve controlled pressure bleed passage and having the capability for being used in redundant fashion with other pressure bleed mechanisms such as manifold valves for safely and efficiently bleeding pressure from the bonnet chambers of valves, the conduit sections of wells and other pressure containing mechanisms.
2. Description of the Prior Art
In the case of valves and other pressure containing apparatus, especially pressure control apparatus for wells, it is often appropriate to bleed fluid pressure from closed chambers to enable other functions to take place. For example, it is often necessary to bleed fluid pressure from the bonnet chamber of a valve to enable the valve to be safely opened. As another example, when wire line controlled activities are necessary for wells, valves and conduit sections will typically be bled of pressure to enable installation of the wire line, wire line blowout preventers etc. The typical procedure for bleeding pressure from a closed chamber is to isolate a pressure containing chamber from a pressure source typically requires closure of an upstream valve. A pressure bleed conduit in communication with the closed pressure containing chamber by a conventional pressure by-pass stud to which the pressure bleed conduit is connected will then be controlled by one or more manifold valves which are opened to accomplish pressure bleeding.
While bleeding of fluid pressure from bonnet chambers and other pressure containing apparatus is efficiently controlled by conventional bleed valves, a number of problems exist that may influence the safety of the fluid handling system. One important consideration is that the pressure bleed system from the pressurized bonnet chamber or other pressure containing apparatus is always under pressure, with this pressure being controlled only by the manifold valve or other pressure bleed valve mechanism. In the event the bleed conduit of the pressure bleed system should be damaged and should begin to leak upstream of the manifold valves, there may be no way to safely stop the leakage without shutting down the pressure containing and controlling system. In the case of high pressure wells for controlling production of petroleum products, the well would need to be shut in by closing a master valve to allow the bleed control valve to be repaired or replaced, also, in the case of oil wells, release of potentially combustible petroleum products could result in various types of hazards, including fire, release of toxic gases, well blowout, contamination of the environment, etc. When the pressure bleed system has a single control valve such as a manifold valve, debris, such as sand, pipe scale and other particulate from the flowing fluid may interfere with complete closure of the valve. In this case the valve can have high pressure leakage of fluid across its seat, causing the seat or the valve element or both to be eroded and permanently damaged, so that its replacement or repair is necessary. Especially in the case of high pressure wells, it is desirable that the pressure bleed system have valve redundancy so that, in the event of leakage of the primary pressure bleed valve, a secondary bleed control valve may be closed to ensure against leakage in the pressure bleed system. This will permit the primary pressure bleed valve to be restored by repair, replacement or by simply cleaning away debris that interferes with its sealing capability. It is also considered desirable that the redundant secondary pressure bleed control valve be protected by structural components so that it cannot be easily damaged. The secondary bleed control valve should also be so located that leakage of a bleed conduit connected to a by-pass stud can be simply and efficiently stopped so that the integrity of the bleed conduit or its connection can be restored.